A micro-lens is a micro-miniature optical lens, typically having a diameter less than 3 millimeters. Micro-lenses are coming into increasing use with laser diodes and laser diode arrays. Mounting micro-lenses requires a design that will maintain the alignment of the laser source and the micro-lens, with sub-micron tolerance. In addition to requiring the micro-lens to be mounted adjacent to the edge of the laser die, many designs must ensure that the micro-lens maintains a stable position notwithstanding thermal cycling.
Much of the difficulty in mounting the lens adjacent to the laser source results from a wicking of the epoxy or solder used to mount the lens thereto. The wicking of the epoxy or solder often obscures the laser's emission aperture. A prior art attempt to mount the lens adjacent to the laser source is shown in U.S. Pat. No. 5,084,895 to Shimada et al. In Shimada et al., the lens in mounted adjacent to the laser source by etching both, in a planar fashion, onto the same substrate. In U.S. Pat. No. 4,079,904 to Comerford et al., the laser source and micro-lens are mounted onto two structural members so that they are optically coupled adjacent to one another by providing a complementary pattern of matching grooves in the members.
Further, there has been great difficulty, in the past, with maintaining the optical alignment of the laser source and the micro-lens over a change in temperature. Often, the laser source and micro-lens will become misaligned due to differences in the magnitude of expansion of the materials from which they are manufactured. If the thermally induced mismatch causes the lens, its support, or its bonding material (i.e. epoxy) to distort permanently, the excess lens material will cause it to "sag". If the lens and mount combinations change temperature (which may be the case under some operation condition), the thermal expansion mismatches between the lens and its mount can also cause sagging. This results in a substantial loss in illumination intensity, a reduction in beam quality or a change in beam direction.
The amount of "sag" that is acceptable depends upon the parameters of the microlens. For example, shaped microlenses can tolerate misalignments of 1 micrometer or less. Cylindrical microlenses typically have tolerances of 1 to 10 micrometers. However, the prior art has failed to provide a structure that maintains the alignment of the micro-lens with the laser source of a semiconductor laser assembly subjected to a change in temperature, i.e., thermal cycling.